A heat recovery installation is suitable for recovering heat from a relatively hot source of heat to a relatively cold source of heat and vice versa. The device is particularly suitable for recovering heat from used ventilation air from buildings. In this case, the fresh ventilation air coming in from outside is heated by means of the discharged used ventilation air if the outside air is colder than the air in the building. Conversely, the device can cool down incoming fresh air by means of the outflowing used air if the air outside is hotter than the air inside the building.
A car radiator is a known heat exchanger which cools the coolant in the engine by means of air which flows through it. Just before the air entry point the air has the same temperature as the ambient air, and a few centimeters downstream the air has a much higher temperature at the air exit point as a result of having cooled the coolant in the radiator. Due to the velocity of the air, the heat in the hotter air downstream cannot flow to the colder air upstream and the radiator forms an optimum barrier against heat which would like to flow from the hot side to the cold side. Such a barrier is also referred to as a superadiabatic flow. The flow is superadiabatic if the velocity of the inflowing air is greater than the velocity of the heat, which wants to flow from hot to cold. (Pushing a metal rod sufficiently quickly into a hot liquid will not result in scalding of your hands). The heat velocity of a substance is expressed in Péclet (Pe), which has to be significantly greater than 1 (Pe>>1) in order to achieve a good superadiabatic flow, with the downstream heat insulation being optimal.
A known superadiabatic burner preheats the inlet air of a radiation burner for a thermophotovoltaic cell (TPV) [reference: K. Hanamura, TPV Power Generation using Super-Adiabatic Combustion in Porous Quartz Glass]. In this case, the TPV converts the radiation into electrical energy. As the TPV operates at room temperature, a transparent insulation has to be provided between the TPV and the burner. With the known burner, porous quartz walls are used for this purpose, as a result of which the inlet air flows superadiabatically and also recovers the heat radiation loss in the quartz in the process. Due to the superadiabatic flow, the heat of the burner cannot flow against the flow and the TPV remains at room temperature. This burner has the drawback that a significant amount of heat is lost in the exhaust of the burner which cannot be recovered through the inlet air which flows through the porous quartz walls.
Known heat recovery installations for ventilation air consist of a heat exchanger, in which the discharged ventilation air flows on one side of a wall and the inflowing ventilation air flows on the other side. The heat is in this case exchanged according to the counterflow principle. Examples thereof are compact heat exchangers, heat wheels and the Fiwihex. The counterflow principle, in which the discharged air flows in the direction opposite to that of the fresh air, is necessary in order to achieve an efficiency in excess of 95% in practice. In co-current, for example, the maximum efficiency which can be achieved theoretically is only 50%, and in crosscurrent the maximum efficiency which can be achieved, depending on the angle at which crossing takes place, is theoretically between 50 and 100%. The known heat recovery installations for ventilation air are not suitable for insulating large surface areas by means of superadiabatic flow and for collecting heat from (sun)light.
Known solar collectors are solar boilers which are insulated against heat loss using glass wool or foam on the shadow side and transparent channel plate on the sun side. Channel plate consists of several plates which are arranged parallel to one another and between which air cavities are present. The plates are kept at a distance from one another by means of partitions which are arranged parallel to one another. Thus, channels are created in the air cavities between the partitions and the plates which run parallel to one another. In the case of two plates, one layer of channels is thus formed (channel layer) or a single-channel plate, and with several plates n, n−1 channel layers or an (n−1) channel plate is created. Thus, four plates result in a three-channel plate. Although channel plates insulate reasonably well and are therefore widely used for passive heating of glasshouses and greenhouses, much of the heat of the incident and collected (sun)light is lost, particularly in winter when there is little natural light and the environment is cold.
Due to environmental problems and the fact that the supply of fuels is finite, there is an increasing need to recover heat and use solar heat, as well as to store it. In addition, due to the improved insulation of buildings, the need for central ventilation with increasingly large flow rates becomes greater and the demand will rise for compact and inexpensive integrated heating and ventilation installations, which produce heat in the winter in a highly efficient manner, both from (sun)light and through the recovery of ventilation air, and using as little as possible of the increasingly expensive and environmentally polluting primary energy. In addition, there is an increasing demand to achieve cooling in the summer using as little as possible of the increasingly expensive and environmentally polluting primary energy.